Study on dual-loop λ control model of gasoline engine based on unilateral time delay PI controller

For engine equipped with dual switch-type oxygen sensors upstream and downstream of the Three-Way Catalyst (TWC), an innovative dual-loop control model of excess air ratio is proposed here. The front oxygen sensor is used to perform PI feedback control of the closed-loop control factor that makes λ ripple periodically in the vicinity of 1. The rear sensor is used to monitor and correct the λ drift in real-time. Depending on the deviation extent of the rear oxygen sensor voltage from its reference value, an unilateral time delay is applied to the closed-loop control factor at either lean-to-rich burst or rich-to-lean burst of front oxygen sensor to compensate the λ offset. In this way, λ can be controlled precisely with the optimum operating window around 1. ASCET software is used to graphically design the dual-loop PI controller based on finite state machine and automatically generate C codes that run on MPC5634 hardware platform. Engine bench tests of traditional closed-loop control and dual-loop control using front oxygen sensors with different drifting directions were conducted to make comparisons. The experimental results showed that the new dual-loop controller can still achieve a high-accuracy in λ control even when the front oxygen sensor behaved abnormally.